The present invention relates to a new and distinct blackberry cultivar designated ‘Columbia Giant’ and botanically known as Rubus subg. Rubus Watson. This new blackberry cultivar was discovered in Corvallis, Oreg. in July 2008 and originated from a cross between the female blackberry plant ‘NZ 9629-1’ (unpatented) and the male parent blackberry plant ‘ORUS 1350-2’ (unpatented). ‘Columbia Giant’'s spinelessness is derived from ‘Lincoln Logan’ (unpatented) that can be found as a parent four and five generations back in ‘Columbia Giant’'s pedigree. ‘Columbia Giant’ was selected from the same population as ‘Columbia Star’ (U.S. Plant patent application Ser. No. 13/815,074, now U.S. Plant Pat. No. 25,532). The original seedling of the new cultivar was asexually propagated at a nursery in Benton County, Oreg. The new cultivar was established in vitro from a cane cutting and microcuttings have been taken and rooted from this sort of culture. The present invention has been found to be stable and to reproduce true to type through successive asexual propagations.